feat: lightbox EXIF panel, tag management, reorderable albums

EXIF info panel:
- New on-demand get_image_exif command (kamadak-exif) returning camera/lens/
  aperture/shutter/ISO/focal-length and decimal GPS; read from the file when the
  lightbox opens (no DB schema change, works on already-indexed images).
- Lightbox shows a Camera panel; GPS opens the location in the browser via
  OpenStreetMap (adds opener:allow-open-url capability).

Tag management:
- Backend rename_tag (rename, or merge when the target exists) and delete_tag
  (library-wide), both clearing the tag-cloud cache; store actions invalidate
  tag caches, refresh Explore, and re-point/refresh an active tag-search.
- Explore -> Tag Cloud gains a Manage mode: a flat list with per-tag rename/
  merge/delete.

Albums:
- Drag-to-reorder in the sidebar via framer-motion Reorder with a hover handle;
  order persists through the existing reorder_albums command.

Reads live store order on drag end and robustly derives GPS hemisphere from raw
EXIF ref bytes (review follow-ups). CHANGELOG updated.

src-tauri/capabilities/default.json

@@ -6,6 +6,7 @@
   "permissions": [
     "core:default",
     "opener:default",
+    "opener:allow-open-url",
     "dialog:default",
     "dialog:allow-open",
     "fs:default",